In the medical field, a lead foil (sheet) has been used widely for shielding X-rays or radiation. Lead is favorable as a material from a viewpoint of shielding X-rays or radiation (see Patent Document 1), however, it is not preferable from a viewpoint of an influence on environment, and the use thereof is strictly restricted for general parts and general apparatuses, and even in the case of medical parts and medical apparatuses having therein lead, “regimented disposal” is required, thus, searching for alternative material for lead is urgent business, especially in the field related to medical apparatuses.
Further, the aforesaid lead sheet is generally attached on each of members on the periphery of the recording medium (see Patent Document 2, for example). The lead sheet is structured so that a distance between the recording medium and a surface of the lead sheet is constant. For example, even in the case of a cassette for medical X-ray radiography, a lead sheet has been arranged between a recording medium such as a sheet film and a stimulable phosphor plate and a back plate of the cassette, for eliminating an influence of rear scattered X-ray in the course of radiography.
FIG. 7 shows a conventional example of the cassette for medical X-ray radiography. The conventional cassette for medical X-ray radiography shown in FIG. 7 is composed of front plate 201 that is positioned on the side where X-rays are irradiated, back plate 202 positioned on the side opposite to the front plate and of frame 203 positioned on the side of the outer circumference, and in the cassette, there housed recording medium plate 200 that is a sheet film or a stimulable phosphor plate on which an X-ray image is recorded. For eliminating an influence of rear scattered X-ray in the course of radiography, lead sheet 204 is arranged on an inner surface of back plate 202 and a distance between the recording medium plate 200 and a surface of lead sheet 204 is organized to be uniform.
When this lead sheet 204 provided on a cassette back plate 202 with a two-sided adhesive tape is not stuck uniformly and air bubbles are partially generated, it needs to be stuck again because an image is influenced. In this case, the lead sheet peeled off once is not flat enough and cannot be used for sticking again, thus, it has been necessary to use a fresh lead sheet, resulting in disposal of lead sheets.
A two-sided adhesive tape itself has its own thickness which is necessary to be compensated by the thickness of the back plate or of the recording medium itself, in order to keep the outer dimension of the cassette unchanged. Therefore, consideration on the design of the cassette has been needed to maintain the mechanical strength of the cassette, for example, the stiffness.
(Patent Document 1) Japanese Patent Publication Open to Public Inspection (hereafter referred to as JP-A) No. 59-17198
(Patent Document 2) JP-A No. 7-20591